Directional speaker control system

ABSTRACT

In a directional speaker control system for realizing good sound localization by correcting the directivity of a directional speaker, adapted to an audio surround system in which a desired sound is reflected on a wall surface or a sound reflection board so as to produce a virtual speaker, a first directional speaker emits a first sound toward the wall surface or sound reflection board so that the reflected sound reaches a prescribed listening position, and a second directional speaker emits a second sound, which comes to have an inverse phase with respect to an audio element of the first sound reaching the listening position directly, toward the listening position. Thus, it is possible to adequately dampen the audio element (particularly, low-frequency components) emitted directly toward the listening position from the first directional speaker; hence, it is possible to realize good sound localization.

This application is a U.S. National Phase Application of PCTInternational Application PCT/JP2004/014437 filed on Sep. 24, 2004.

TECHNICAL FIELD

This invention relates to directional speaker control systems in whichsounds emitted from directional speakers such as array speakers arereflected on wall surfaces or sound reflection boards so as to producevirtual speakers.

BACKGROUND ART

Recently, various audio sources have been distributed and provided inthe open market; and DVDs (digital versatile disks) store multi-channelaudio signals of 5.1 channels, for example. Digital surround systems forreproducing audio sources have come to be widespread among generalhouseholds. FIG. 14 is a plan view showing an example of a layout ofspeakers in a digital surround system, wherein reference numeral Zonedesignates a listening room for performing audio surround playback;reference numeral U designates a listening position; reference numeralSP-L designates a speaker for reproducing a main left signal L;reference numeral SP-R designates a speaker for reproducing a main rightsignal R; reference numeral SP-SL designates a speaker for reproducing arear left signal SL; reference numeral SP-SR designates a speaker forreproducing a rear right signal SR; reference numeral SP-SW designates asub-woofer for reproducing a sub-woofer signal (a low-frequency signal)LFE; and reference symbol MON designates a video device such as atelevision receiver.

The digital surround system of FIG. 14 can effectively produce varioussound fields. Since plural speakers are separately arranged in thelistening room Zone, the digital surround system has drawbacks in thatin order to arrange surround rear speakers SP-SL and SP-SR in the rearof the listening position U, wiring lengths between the speakers must beincreased, and the arrangement of the rear speakers SP-SL and SP-SR islimited by the shape of the listening room Zone and the arrangement offurniture.

In order to solve the aforementioned drawbacks, rear speakers are formedusing directional speakers having sharp directivities and arranged infront of the listening position, while a sound reflection board isarranged in the rear of the listening position. There is provided anaudio surround system in which surround-channel sounds emitted fromdirectional speakers are reflected on sound reflection boards so as todemonstrate an effect similar to an effect realized by arranging rearspeakers in the rear of the listening position. This is disclosed inJapanese Unexamined Patent Application Publication No. H06-178379, forexample. FIG. 15 is a plan view showing an example of a layout ofspeakers in an audio surround system disclosed in this JapaneseUnexamined Patent Application Publication, wherein reference numeralsB-L and B-R designate sound reflection boards.

It is possible to use a method in which a wall surface positioned in therear of a listening room is used as a sound reflection board as shown inFIG. 16. In a three-dimensional stereo audio playback method disclosedin Japanese Unexamined Application Publication No. H03-159500, forexample, an array speaker is used to produce virtual sound sources inthe space. By use of this technology, it is possible to produce virtualspeakers in the rear of a listening position.

As described above, it is possible to produce virtual speakers in therear of a listening position by arranging sound reflection boards in therear of the listening position or by using a wall surface of a listeningroom as a sound reflection board. However, this method may be stronglyaffected by sound directly emitted from a directional speaker arrangedin front of the listening position; hence, it has a problem in thatsound localization similar to sound localization realized by arrangingrear speakers in the rear of the listening position cannot be affected.This is because human ears are shaped to easily pick up sound from thefront, and the Haas effect may occur because direct sound reaches theears of the listener first since a distance for directly transmittingsound to the listener without the intervention of a wall is shorter thana distance for transmitting sound emitted from a directional speakerafter reflection on a wall.

This invention is made to solve the aforementioned problems; hence, itis an object of the invention to provide a directional speaker controlsystem adapted to an audio surround system in which sound emitted from adirectional speaker is reflected on a wall surface or a sound reflectionboard so as to produce virtual speakers, wherein good sound localizationis realized by correcting the directivity of the directional speaker.

DISCLOSURE OF THE INVENTION

This invention provides a directional speaker control system in whichsound emitted from a directional speaker having sharp directivity isreflected on a wall surface or a sound reflection board so as to producevirtual speakers. It includes a first directional speaker for emitting afirst sound toward the wall surface or sound reflection board, and asecond directional speaker for emitting a second sound which comes tohave an inverted phase at a listening position compared with the phaseof an audio element of the first sound reaching the listening positiondirectly, wherein the directivity of the first directional speaker iscorrected based on the second sound.

For example, the first directional speaker such as an array speakerhaving high directivity is arranged at a prescribed position, and thesound thereof is emitted towards and reflected on the wall surface orthe sound reflection board, which is positioned at a position differentfrom the position of the first directional speaker, thus realizing soundlocalization as if a speaker existed at the position of reflection. Thefirst sound emitted from the first directional speaker contains an audioelement reaching the listening position directly; hence, there occurs aphenomenon in which a sound image to be localized at a prescribedposition of the wall surface or the sound reflection board is localizedin proximity to the first directional speaker. Since it is difficult toincrease energy of sound reflected on the wall surface or the soundreflection board, the audio element reaching the listening positiondirectly from the first directional speaker is dampened using the secondsound emitted from the second directional speaker.

In a concrete example of the constitution of the directional speakercontrol system of this invention, a single array speaker device isdivided into a first directional speaker and a second directionalspeaker as described above.

The second directional speaker emits low-frequency components of soundonly as the second sound.

In this invention, an audio element of the first sound emitted from thefirst directional speaker and reaching the listening position directlyis dampened using the second sound emitted from the second directionalspeaker; hence, compared with the audio element reaching the listenerfrom the first directional speaker directly, it is possible to enhancethe reflected sound, which is produced by reflecting the first sound onthe wall surface or the sound reflection board and then letting it reachthe listener. Thus, it is possible to realize good sound localizationsimilar to that realized by arranging speakers in the rear of thelistener. In addition, the first directional speaker and the seconddirectional speaker can produce virtual rear speakers. This eliminatesthe necessity of arranging rear speakers in the rear of the listeningposition; hence, it is possible to reduce wiring distances between thespeakers.

A single array speaker is used to realize both the first directionalspeaker and second directional speaker; hence, even when another arrayspeaker is used to perform sound cancellation using inverse phases, itis possible to prevent the listener from feeling uncomfortableness inhearing.

Furthermore, the sound subjected to dampening control by the seconddirectional speaker is limited to a low-frequency sound; hence, it ispossible to effectively dampen an audio element of the first soundemitted from the first directional speaker and reaching the listeningposition directly; and it is possible to avoid a problem in which theaudio element to be dampened at the listening position increases inlevel unexpectedly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the constitution of a directionalspeaker control system in accordance with a first embodiment of thisinvention;

FIG. 2 is a block diagram showing internal constitutions of first andsecond directional speakers shown in FIG. 1;

FIG. 3 is a block diagram showing the constitution of a directionalspeaker control system in accordance with a second embodiment of thisinvention;

FIG. 4 is a block diagram showing internal constitutions of first andsecond directional speakers in the second embodiment;

FIG. 5 is a drawing for explaining a directivity control method for thedirectional speaker of the second embodiment;

FIG. 6 is a graph of sound pressure distribution showing the directivityof the first directional speaker of the second embodiment;

FIG. 7 is a graph of sound pressure distribution showing the directivityof sound emitted in a front direction from the first directional speakerof the second embodiment;

FIG. 8 is a graph of sound pressure distribution realized when the soundemitted from the first directional speaker is dampened using the soundemitted from the second directional speaker in the second embodiment;

FIG. 9 is a block diagram showing the constitution of a directionalspeaker control system in accordance with a third embodiment of thisinvention;

FIG. 10 is a block diagram showing internal constitutions of twodirectional speakers in the third embodiment;

FIG. 11 is a graph of sound pressure distribution showing thedirectivity of sound emitted in a front direction from a firstdirectional speaker in a fourth embodiment;

FIG. 12 is a graph of sound pressure distribution realized when thesound emitted from the first directional speaker is dampened using thesound emitted from a second directional speaker in the fourthembodiment;

FIG. 13 is a block diagram showing internal constitutions of first andsecond directional speakers in a directional speaker control system inaccordance with a fifth embodiment of this invention;

FIG. 14 is a plan view showing an example of a layout of speakers in adigital surround system;

FIG. 15 is a plan view showing an example of a layout of speakers in anaudio surround system in which rear speakers are arranged in front of alistening position; and

FIG. 16 is a plan view showing an example of a layout of speakers in anaudio surround system in which a wall positioned in the rear of alistening position is used as a sound reflection board.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of this invention will be described in detail byway of examples with reference to the accompanying drawings.

First Embodiment

FIG. 1 is a block diagram showing the constitution of a directionalspeaker control system (i.e., a surround system) in accordance with afirst embodiment of this invention. FIG. 1 shows only the constitutionregarding a surround channel (i.e., a rear left signal SL or a rearright signal SR), and it does not show the constitution regarding a mainchannel (i.e., a main left signal L or a main right signal R).

The directional speaker control system according to the first embodimentof this invention includes a first directional speaker 1 for emitting afirst sound S1 towards a wall surface of a listening room or a soundreflection board 3 and a second directional speaker 2 for emitting asecond sound S2 whose phase is inverse to that of an audio element S1 aof the first sound S1 which reaches a listening position U directly.

FIG. 2 is a block diagram showing internal constitutions of thedirectional speakers 1 and 2. The first directional speaker 1 includes adelay circuit 104 for delaying an input surround-channel audio signal(i.e., a rear left signal SL or a rear right signal SR) by a prescribeddelay time T1, a gain adjustment circuit 101 for adjusting a gain of anoutput signal of the delay circuit 104 to a desired level, an amplifier102 for amplifying an output signal of the gain adjustment circuit 101,and a speaker 103 driven by the output of the amplifier 102.

The second directional speaker 2 includes an inversion circuit 201 forinverting the phase of the surround-channel audio signal, a delaycircuit 202 for adjusting a delay time applied to an output signal ofthe inversion circuit 201 such that the audio element S1 a of the firstsound S1 reaching the listening position U from the directional speaker1 directly is canceled out by the second sound S2 emitted from thedirectional speaker 2, a gain adjustment circuit 203 for adjusting again of an output signal of the delay circuit 202 such that the audioelement S1 a is canceled out by the second sound S2, an amplifier 204for amplifying an output signal of the gain adjustment circuit 203, anda speaker 205 driven by the output of the amplifier 204.

Next, the operation of the directional speaker control system of thepresent embodiment will be described in detail.

In the directional speaker 1, the delay circuit 104 delays asurround-channel audio signal by the prescribed delay time T1; the gainadjustment circuit 101 adjusts the gain of the output signal of thedelay circuit 104; and the amplifier 102 amplifies the output signal ofthe gain adjustment circuit 101 so as to drive the speaker 103. Thespeaker 103 emits a sound S1 corresponding to a sound beam having sharpdirectivity, which is reflected on the wall surface or the soundreflection board 3 so that a reflected sound Sk reaches the listeningposition U. Thus, the wall surface or the sound reflection board 3functions as a virtual rear speaker. Strictly speaking, the sound outputof the speaker 103 does not form a sound beam; hence, audio elements S1a, S1 b, and S1 ceach having a low sound pressure compared with thesound pressure of a main audio element of the sound S1 are emitted indirections each differing from the emission direction of the sound S1.Within these audio elements, the audio element S1 a emitted towards thelistening position U directly is dampened using the sound S2 emittedfrom the directional speaker 2.

The inversion circuit 201 of the directional speaker 2 inverts thepolarity of the surround-channel audio signal in order to realize aninverse phase for the audio signal in the directional speaker 1. Theoutput signal of the inversion circuit 201 is supplied to the amplifier204, in which it is amplified, via the delay circuit 202 and the gainadjustment circuit 203. The speaker 205 is driven by the output signalof the amplifier 204, thus emitting the sound S2. The delay time of thedelay circuit 202 and the gain of the gain adjustment circuit 203 areadjusted in advance such that the audio element S1 a reaching thelistening position from the directional speaker 1 directly is canceledout by the sound S2 emitted directly to the listening position U fromthe directional speaker 2.

The audio element S1 a emitted from the speaker 103 of the directionalspeaker 1 reaches the listening position U with a delay time LNA/V,wherein LNA represents a distance from the speaker 103 to the listeningposition U, and V represents the speed of sound. Similarly, the sound S2emitted from the speaker 205 of the directional speaker 2 reaches thelistening position with a delay time LNB/V, wherein LNB represents adistance from the speaker 205 to the listening position U. Hence, thereis a time difference (LNA−LNB)/V between an arrival time of the audioelement S1 afrom the speaker 103 at the listening position U and anarrival time of the sound S2 from the speaker 205 at the listeningposition U. That is, an audio signal whose phase is inverted in thedirectional speaker 2 is delayed by (LNA−LNB)/NV+T1, so that the audioelement S1 a and the sound S2 have mutually inverted phases at thelistening position U; as a result, it is possible to dampen the audioelement S1 a. As described above, the delay time of the delay circuit202 is adjusted in advance to compensate for the difference between thedistances LNA and LNB such that the sound S2 emitted from thedirectional speaker 2 comes to have a desired phase at the listeningposition U.

The aforementioned description is given with attention given to phasesonly. It is possible to calculate sound pressure of the audio element S1a at the listening position U based on the directivity of thedirectional speaker 1 and the distance LNA. Similarly, it is possible tocalculate sound pressure of the sound S2 at the listening position U. Byadjusting the gain of the gain adjustment circuit 203 based oncalculation results, it is possible to control a dampening value for theaudio element S1 a; hence, it is possible to control the audio elementS1 a to make it have a desired sound pressure at the listening positionU.

As described above, the present embodiment can dampen the audio elementS1 a reaching the listener from the directional speaker 1 directly byuse of the sound S2 emitted from the directional speaker 2. That is, itis possible to relatively enhance the sound Sk, which reaches thelistener after being reflected on the wall surface or the soundreflection board 3, compared with the audio element S1 a reaching thelistener from the directional speaker 1 directly. Thus, it is possibleto realize sound localization similar to that realized by arranging rearspeakers in the rear of the listener.

Second Embodiment

Next, a second embodiment of this invention will be described. FIG. 3 isa block diagram showing the constitution of a directional speakercontrol system of the second embodiment. The second embodiment ischaracterized in that array speakers are used for a first directionalspeaker 11 and a second directional speaker 12 respectively. FIG. 4 is ablock diagram showing internal constitutions of the directional speakers11 and 12.

The first directional speaker 11 includes a delay circuit 111 forapplying a delay time, corresponding to the directivity (i.e., a focalposition of a sound beam) to be realized, to an input surround-channelaudio signal, plural gain adjustment circuits 112 (112-1 to 112-n) foradjusting gains of output signals of the delay circuit 111 to desiredgains, plural amplifiers 113 (113-1 to 113-n) for amplifying outputsignals of the gain adjustment circuits 112, and plural speakers 114(114-1 to 114-n) driven by the amplifiers 113.

The second directional speaker 12 includes an inversion circuit 211 forinverting the phase of the surround-channel audio signal, a delaycircuit 212 for applying a delay time to an output signal of theinversion circuit 211 so as to realize directivity in which the secondsound S2 is emitted from the directional speaker 12 towards thelistening position U and so as to cancel out the audio element S1 a ofthe first sound, emitted directly to the listening position U from thefirst directional speaker 11, by use of the second sound S2, plural gainadjustment circuits 213 (213-1 to 213-m) for adjusting gains of outputsignals of the delay circuit 212 so that the audio element S1 a iscanceled out by the second sound S2, plural amplifiers 214 (214-1 to214-m) for amplifying output signals of the gain adjustment circuits213, and plural speakers 215 (215-1 to 215-m) driven by the amplifiers214. In the above, the first directional speaker 11 arrays the pluralspeakers 114 whose number is n (where n is an integer that is two orhigher) in a two-dimensional manner, and the second directional speaker12 arrays the plural speakers 215 whose number is m (where m is aninteger that is two or higher) in a two-dimensional manner, and n=m orn≠m.

Next, the operation of the directional speaker control system of thesecond embodiment will be described in detail. The first directionalspeaker 11 performs directivity control such that sounds emitted fromthe speakers 114 are directed towards a prescribed wall surface or asound reflection board 3. The directivity control of the firstdirectional speaker 11 will be described with reference to FIG. 5.Herein, reference symbol Z designates an circular arc that is separatedfrom a position P on the wall surface or the sound reflection board 3 bya distance D; and virtual speakers 115 (115-1 to 115-n) denoted bydotted circles are arranged at intersection points at which linesegments connecting the position P and the speakers 114 (114-1 to 114-n)of the first directional speaker 11 are extended to intersect with thecircular arc Z. Since the same distance D lies between the position Pand the virtual speakers 115, sounds emitted from the virtual speakers115 reach the position P at the same time.

In order to make all the sounds emitted from the speakers 114-i (wherei=1, 2, . . . , n) of the first directional speaker 11 reach theposition P at the same time, it is required that a delay time LAi/Vcorresponding to a distance LAi between each speaker 114-i and itscorresponding virtual speaker 115-i be applied to an input signal of thespeaker 114-i. Based on the aforementioned operation principle of anarray speaker, the delay circuit 111 of the first directional speaker 11applies the delay time LAi/V corresponding to each speaker 114-i to aninput surround-channel audio signal, thus outputting n delayed audiosignals.

The gain adjustment circuits 112-i adjust gains of output signals of thedelay circuit 111; and the amplifiers 113-i amplify output signals ofthe gain adjustment circuits 112-i so as to drive the speakers 114-i.

As described above, by adjusting the delay time applied to an audiosignal per each speaker 114-i, the sound emitted from the firstdirectional speaker 11 can be controlled in directivity; hence, it ispossible to make the sounds emitted from the speakers 114-i have thesame phase at a single point (i.e., a focal point) in space. The firstsound S1 emitted from the directional speaker 11 is reflected on thewall surface or the sound reflection board 3, so that the reflectedsound Sk reaches the listening position U.

FIG. 6 is a graph of sound pressure distribution showing an example ofdirectivity realized by the first directional speaker 11. FIG. 6 showscontour lines of sound pressure levels measured upon generation of asingle-frequency sound (e.g., 1 kHz) with respect to an X-Y plane, andit shows variations of sound pressure levels when plural speakers 114are arrayed at 0 cm on the X-axis. By using an array speaker for thefirst directional speaker 11, it is possible to realize intensedirectivity (i.e., sound beam) in a direction of the arrow in FIG. 6. Asdescribed for the first embodiment, this shows that certain soundpressures occur in directions other than the direction of the soundbeam.

The present embodiment dampens the audio element S1 a(S1 a-1 to S1 a-n),which is directly emitted towards a listener within audio elementsdispersed in directions differing from the direction of the sound beam,by use of the sound S2 (S2-1 to S2-n) emitted from the seconddirectional speaker 12.

As in the first embodiment, the inversion circuit 211 of the seconddirectional speaker 12 inverts the phase of the aforementionedsurround-channel audio signal.

The delay time of the delay circuit 212 is adjusted in advance such thatthe sound S2 emitted from the second directional speaker 12 is directedtowards the listening position U, and the audio element S1 a emitteddirectly to the listening position U from the first directional speaker11 is canceled out by the sound S2.

In order to simplify calculations, both the directional speakers 11 and12 include the same number of speakers (where n=m), wherein an audioelement S1 a-i emitted to the listening position U from one speaker114-i of the first directional speaker 11 is dampened by use of an audioelement S2-i emitted from one speaker 215-i of the second directionalspeaker 12. For the sake of convenience, the present embodiment is notdesigned to perform precise directivity control in the seconddirectional speaker 12.

With regard to a distance LNAi from the speaker 114-i of the firstdirectional speaker 11 to the listening position U and a distance LNBifrom the speaker 215-i of the second directional speaker 12 to thelistening position U, in order to compensate for a difference betweenthese distances, as in the first embodiment, it is necessary to apply adelay time (LNAi−LNBi)/V to an input signal of the speaker 215-i. Sincethe delay circuit 111 applies a delay time LAi/V to the sound outputfrom the speaker 114-i, it is necessary to apply the delay time LAi/V tothe sound output from the speaker 215-i.

Therefore, the delay circuit 212 of the second directional speaker 12applies delay times defined by {(LNAi−LNBi)+LAi}/V the output signal ofthe inversion circuit 211 so as to generate m delay signals.

The gain of the gain adjustment circuit 213-i is adjusted in advancesuch that the audio element S1 a-i directly reaching the listeningposition U from the speaker 114-i is canceled out by the audio elementS2-i emitted from the speaker 215-i toward the listening position U. Asdescribed in the first embodiment, it is possible to calculate soundpressures of the audio elements S1 a-i and S2-i at the listeningposition U; hence, based on the calculation results, it is possible toadjust the gain of the gain adjustment circuit 213-i.

The amplifier 214-i of the second directional speaker 12 amplifies theoutput signal of the gain adjustment circuit 213-i so as to drive thespeaker 215-i.

As described above, the second embodiment can demonstrate effectssimilar to those of the first embodiment. In general, sound cancellationusing inverse phases may cause feelings of uncomfortableness forlisteners. However, when array speakers are used for the directionalspeakers 11 and 12, they can form sound fields in which sounds ofvarious phases may intermix with each other; hence, even when soundcancellation is performed using inverse phases, there is provided aneffect of not making listeners have feelings of uncomfortableness.

FIGS. 7 and 8 show graphs of sound pressure distributions produced uponexecution of directivity corrections in accordance with the presentembodiment. FIGS. 7 and 8 are graphs each showing contour lines of soundpressure levels measured upon generation of a single-frequency sound(e.g., 500 Hz) with respect to an X-Y plane, wherein a listeningposition is at 0 cm on the X-axis and 300-400 cm on the Y-axis.Specifically, FIG. 7 shows sound pressure distribution that is measuredwhen the first directional speaker 11 emits a sound in a front directionthereof; and FIG. 8 shows sound pressure distribution that is measuredwhen the sound emitted from the directional speaker 11 is dampened by asound of an inverse phase emitted from the second directional speaker12. FIG. 8 shows that sound pressure energy decreases at the listeningposition.

Third Embodiment

Next, a third embodiment of this invention will be described. Theaforementioned first and second embodiments need two directionalspeakers per channel; hence, four directional speakers in total areneeded for a 2-channel surround system. In contrast, the thirdembodiment provides a practical example in which a 2-channel surroundsystem is actualized using two directional speakers. FIG. 9 is a blockdiagram showing a directional speaker control system in accordance withthe third embodiment, which is constituted using directional speakers 21and 22. In FIG. 9, reference numeral 3-L designates a wall surface orsound reflection board that serves as an L-channel virtual rear speaker;and reference numeral 3-R designates a wall surface or sound reflectionboard that serves as an R-channel virtual rear speaker.

The directional speaker 21 functions as a first directional speaker foremitting a sound S1-L toward the wall surface or sound reflection board3-L based on a rear left signal SL, and it also functions as a seconddirectional speaker for canceling out a sound S1 a-R reaching a listenerdirectly from the directional speaker 22 by use of a sound S2-R. Thedirectional speaker 22 functions as a first directional speaker foremitting a sound S1-R toward the wall surface or sound reflection board3-R based on a rear right signal SR, and it also functions as a seconddirectional speaker for canceling out a sound S1 a-L reaching thelistener directly from the directional speaker 21 by use of a soundS2-L.

FIG. 10 is a block diagram showing internal constitutions of thedirectional speakers 21 and 22. In the present embodiment, thedirectional speakers 21 and 22 are constituted using array speakers.

The directional speaker 21 includes a delay circuit 121 for applyingdelay times corresponding to directivities to be realized to an inputrear left signal SL, plural gain adjustment circuits 122 (122-1 to122-n) for adjusting gains of output signals of the delay circuit 121 toprescribed values, an inversion circuit 123 for inverting the phase ofan input rear right signal SR, a delay circuit 124 for applying delaytimes to the output signal of the inversion circuit 123 such that thesound S2-R emitted from the directional speaker 21 is directed towardthe listening position U, and the sound S1 a-R emitted directly towardthe listening position U from the directional speaker 22 is canceled outby the sound S2-R, plural gain adjustment circuits 125 (125-1 to 125-n)for adjusting gains of output signals of the delay circuit 124 such thatthe sound S1 a-R is canceled out by the sound S2-R, plural adders 126(126-1 to 126-n) for adding the output signals of the gain adjustmentcircuits 122 and the output signals of the gain adjustment circuits 125together, plural amplifiers 127 (127-1 to 127-n) for amplifying theoutput signals of the adders 126, and plural speakers 128 (128-1 to128-n) driven by the outputs of the amplifiers 127.

The directional speaker 22 includes a delay circuit 221 for applyingdelay times corresponding to directivities to be realized to an inputrear right signal SR, plural gain adjustment circuits 222 (222-1 to222-n) for adjusting gains of output signals of the delay circuit 221 todesired values, an inversion circuit 223 for inverting the phase of aninput rear left signal SL, a delay circuit 224 for applying a delay timeto the output signal of the inversion circuit 223 such that the soundS2-L emitted from the directional speaker 22 is directed toward thelistening position U, and the sound S1 a-L emitted directly toward thelistening position U from the directional speaker 21 is canceled out bythe sound S2-L, plural gain adjustment circuits 225 (225-1 to 225-n) foradjusting gains of output signals of the delay circuit 224 such that thesound S1 a-L is canceled out by the sound S2-L, plural adders 226 (226-1to 226-n) for adding the output signals of the gain adjustment circuits222 and the output signals of the gain adjustment circuits 225 together,plural amplifiers 227 (227-1 to 227-n) for amplifying the output signalsof the adders 226, and plural speakers 228 (228-1 to 228-n) driven bythe outputs of the amplifiers 227.

The operations of the delay circuit 121 and gain adjustment circuits 122for performing delay and gain adjustment on the rear left signal SL andthe operations of the delay circuit 221 and gain adjustment circuits 222for performing delay and gain adjustment on the rear right signal SR aresimilar to the aforementioned operations of the delay circuit 111 andgain adjustment circuits 112 used in the second embodiment.

In addition, the operations of the inversion circuit 123, delay circuit124, and gain adjustment circuits 125 for performing phase inversion andthen performing delay and gain adjustment on the rear right signal SRand the operations of the inversion circuit 223, delay circuit 224, andgain adjustment circuits 225 for performing phase inversion and thenperforming delay and gain adjustment on the rear left signal SL aresimilar to the aforementioned operations of the inversion circuit 211,delay circuit 212, and gain adjustment circuits 213 used in the secondembodiment.

The delay time of the delay circuit 124 applied to the rear right signalSR whose phase is inverted and which is supplied to the speaker 128-i(where i=1, 2, . . . , n) is adjusted in advance such that the soundS2-R emitted from the speaker 128-i is directed towards the listeningposition U, and the sound S1 a-R emitted directly toward the listeningposition U from the speaker 228-i of the directional speaker 22 iscanceled out by the sound S2-R.

Similarly, the delay time of the delay circuit 224 applied to the rearleft signal SL whose phase is inverted and which is supplied to thespeaker 228-i (where i =1, 2, . . . , n) is adjusted in advance suchthat the sound S2-L emitted from the speaker 228-i is directed towardthe listening position U, and the sound S1 a-L emitted directly towardthe listening position U from the speaker 128-i of the directionalspeaker 21 is canceled out by the sound S2-L. Incidentally, theadjustment methods for the delay times of the delay circuits 124 and 224have been described before in conjunction with the second embodiment.

Next, the adder 126-i adds the output signal of the gain adjustmentcircuit 122-i (corresponding to the rear left signal SL) and the outputsignal of the gain adjustment circuit 125-i (corresponding to the rearright signal SR whose phase is inverted) together. Similarly, the adder226-i adds the output signal of the gain adjustment circuit 222-i(corresponding to the rear right signal SR) and the output signal of thegain adjustment circuit 225-i (corresponding to the rear left signal SLwhose phase is inverted) together.

The amplifier 127-i amplifies the output signal of the adder 126-i so asto drive the speaker 128-i. Similarly, the amplifier 227-i amplifies theoutput signal of the adder 226-i so as to drive the speaker 228-i.

As described above, it is possible to obtain effects similar to those ofthe second embodiment with respect to the 2-channel surround system.This is because an array speaker can simultaneously emit two or moresounds with different directivities. By use of such an array speaker, itis possible to realize a 2-channel surround system using two directionalspeakers.

Fourth Embodiment

The directional speaker control system of the third embodiment isconstituted using two independent directional speakers 21 and 22. It ispossible instead to realize the directional speakers 21 and 22 bydividing a single array speaker. FIGS. 11 and 12 show the results ofdirectivity corrections produced by dividing a single array speaker asdescribed above. FIGS. 11 and 12 show contour lines of sound pressurelevels measured upon generation of a single frequency sound (e.g., 500Hz) with respect to an X-Y plane, wherein a listening position is at 0cm on the X-axis and 300-400 cm on the Y-axis. Specifically, FIG. 11shows sound pressure distribution that is produced when the directionalspeaker 21, which corresponds to a part of an array speaker, emits soundin a front direction thereof. FIG. 12 shows sound pressure distributionthat is produced when the sound emitted from the directional speaker 21is dampened by a sound of an inverse phase emitted from the directionalspeaker 22, which corresponds to another part of the array speaker. Asdescribed above, by dividing a single array speaker, it is possible toarrange the directional speakers 21 and 22 in proximity to each other;hence, it is possible to increase the dampening effect at positionsclose to 0 cm on the X-axis.

Fifth Embodiment

In the aforementioned first to fourth embodiments performing soundcancellation using inverse phases, a wavelength for a main audiofrequency band of 1 kHz maybe set to 30 cm or so, for example; hence,the controllable space should become very small. That is, at the audiofrequency of 1 kHz, the phase may be inverted due to shifting of acontrolled position by 15 cm. This may cause a phenomenon in which soundto be dampened is instead amplified.

By nature, directional speakers are capable of easily realizingdirectivity and producing fine sound beams with respect to sounds ofhigher frequencies, but they have difficulty in narrowing directivitywith respect to sounds of lower frequencies, which tend to spread withease. For this reason, sound beams of higher frequencies emitted fromthe first directional speaker are not weakened so much and reach thewall surface or sound reflection board, while sounds reaching a listenerdirectly have low energy; hence, it is possible to realize good soundlocalization in the rear side with respect to higher frequencies. Incontrast, low-frequency sound may spread in sound pressure distributionso that no sound beam is produced. This weakens the energy of soundreaching the wall surface or sound reflection board but increases theenergy of sound reaching the listener directly. That is, there is a highprobability that sound localization in the front side may occur withrespect to intermediate-frequency sound and low-frequency sound.Therefore, it is effective to limit the sound subjected to dampeningcontrol by the second directional speaker to the low-frequency sound.

FIG. 13 is a block diagram showing internal constitutions of directionalspeakers 1 and 2 incorporated in a directional speaker control system inaccordance with a fifth embodiment of this invention, wherein partsidentical to those shown in FIG. 2 are designated by the same referencenumerals. In the fifth embodiment shown in FIG. 13, a low-pass filter206 for simply filtering low-frequency audio signals whose frequency isseveral hundreds hertz or less is added to the second directionalspeaker 2. It is necessary for the low-pass filter 206 not to causephase rotation; hence, a digital FIR (Finite Impulse Response) filter isused.

Since the sound subjected to dampening control by the second directionalspeaker 2 is limited to low-frequency sound, the present embodiment caneffectively dampen the sound emitted directly toward the listeningposition from the first directional speaker 1. In addition, it ispossible to avoid a problem in which the sound (mainly, thehigh-frequency sound) to be dampened at the listening position isunintentionally increased.

Incidentally, when the aforementioned constitution of the fifthembodiment is adapted to the second embodiment, it is necessary toadditionally provide a low-pass filter at a position preceding the delaycircuit 212 (e.g., at a position between the inversion circuit 211 andthe delay circuit 212) in the directional speaker 12 shown in FIG. 4.When it is adapted to the third and fourth embodiments, it is necessaryto additionally provide a low-pass filter at a position preceding thedelay circuit 124 or 224 (e.g., at a position between the inversioncircuit 123 or 223 and the delay circuit 124 or 224) in the directionalspeaker 21 or 22.

As stated heretofore, this invention is not necessarily limited to theaforementioned embodiments; hence, variations and changes within thescope of the invention may be embraced by this invention.

1. A directional speaker control system for producing an audio surroundsound, said directional speaker control system comprising: a firstdirectional array speaker unit having a plurality of first directionalspeakers arranged in an array each for emitting a first sound toward awall surface or sound reflection board; and a second directional arrayspeaker unit having a plurality of second directional speakers arrangedin an array each for emitting a second sound with an inverse phasedirectly to a prescribed listening position, without reflecting thesecond sound from any wall surface or sound reflection board, withrespect to an audio element of the first sound directly reaching theprescribed listening position, wherein each of the first and seconddirectional array speaker units further includes a delay circuit fordelaying the sound signal, a gain adjustment circuit for eachdirectional speaker for adjusting a gain of an output signal of thedelay circuit, and an amplifier for each directional speaker foramplifying an output signal from the gain adjustment circuit and drivingthe respective directional speaker, wherein the first and seconddirectional array speaker units generate sound fields having variousphases intermixed with each other, wherein the second sound from thesecond directional array speaker unit dampens the audio element of thefirst sound from the first directional array speaker unit directlyreaching the prescribed listening position, wherein the first and seconddirectional array speaker units both receive a same sound signal,wherein the second directional array speaker unit includes an inversioncircuit that inverts the sound signal to generate the second sound atthe inverse phase, and wherein the delay circuit of the seconddirectional array sneaker unit adjusts the delay applied to the soundsignal based on the amount of delay applied to the sound signal in thefirst directional array speaker unit so that the second sound directlyarrives at the prescribed listening position at the same time as theaudio element of the first sound directly reaching the prescribedlistening position.
 2. The directional speaker control system accordingto claim 1, wherein the first directional array speaker unit and thesecond directional array speaker unit are composed of a single arrayspeaker unit having a plurality of directional speakers arranged in anarray, with the directional speakers divided among the first and seconddirectional array speaker units.
 3. The directional speaker controlsystem according to claim 1, wherein the second directional arrayspeaker unit emits only a low-frequency sound as the second sound.